Olefins, like saturated hydrocarbons, aromatics and chlorohydrocarbons, are by-products in the direct synthesis of methylchlorosilanes by the Muller-Rochow method from silicon and chloromethane at 250.degree. to 300.degree. C. using copper catalysts. In contrast to alkanes, olefins are reactive due to their carbon-carbon double bond and can lead to impairment in a number of subsequent processes. For example, they are capable of adding on HCl which is eliminated when exposed to heat. The HCl split off can lead to inhibition of catalysts, to corrosion of containers and plant, and to acid-catalyzed side reactions in processes or at places where participation of HCl should actually be excluded. Olefins themselves may also have an inhibiting action, for example on noble metal catalysts during hydrosilylation.
Attempts have been made to remove olefins as far as possible by distillation. However, the boiling points are often so close to the boiling points of monomeric organochlorosilanes that removal cannot be carried out with an acceptable expenditure.
EP-A 310 258 describes a process for reducing the content of olefins in methylchlorosilanes in which the olefins are reacted with methylchlorosilanes containing hydrogen atoms bonded directly to silicon (H-silanes) in the presence of a dissolved platinum catalyst to give silaalkanes. For a complete conversion, the process requires H-silanes in excess, which, if they have been added additionally to the original silane stream also have to be removed again. The silaalkanes must also be removed, since they usually contain reactive groups, such as Si--Cl.
There was the object of providing a process for the removal of olefins from the silanes or silane mixtures obtained during methylchlorosilane synthesis, in which only substances which can easily be removed are introduced into the silanes or silane mixtures.